It is known that mobile communication networks consist of a wireless radio network part and a fixed core network part. The wireless radio network part serves an area by enabling mobile stations in that area to wirelessly communicate with base stations. The base stations are connected to the fixed core network part.
In “Akari, K., ‘Fundamental problems of nation-wide mobile radio systems’, Review of the Electrical Communication Laboratory, Vo. 16 (1968), 357–373” and “MacDonald, V. H., ‘The Cellular Concept’, The Bell System Technical Journal, Vol. 58 (1979), 15–41” the area to be served is subdivided into uniform hexagons called cells, with a base station being positioned in the center of a cell. In the simplest case, signals are emitted via omnidirectional antennas from this center. Nowadays this is normally a triple sectorization, i.e. the cell is subdivided into three sectors via separate antennas fixed on the base station with each a 120-degree aperture angle. Each sector has a certain capacity, i.e. an average maximum number of mobile devices that can be served simultaneously per radio-frequency carrier in the sector.
The original homogenous cellular concept is generalized in several directions. An adaptation of the cell size to different traffic densities by reducing the diameter (cell splitting) has already been described in ‘The Cellular Concept’.
In “Lorenz, R. W., ‘Kleinzonennetze für den Mobilfunk’, Nachrichtentechnische Zeitschrift, Vol. 31 (1978), 192–196” it is proposed to subdivide a cell into six sectors of 60 degrees each, as can be found in several mobile radio networks. In “Halpern, S. W., ‘Reuse partitioning in cellular systems’, Proc. 33rd IEEE Vehicular Technology Conference (1983), 322–327” omnidirectional and triple sectorized systems are subdivided once again into concentric rings. This concept is subsequently technically implemented by Nokia in the form of the “Intelligent Underlay-Overlay” feature for the GSM system. The same number of sectors in each of the concentric rings is characteristic of this concept.
In practice, there are more or less substantial deviations from the geometrical ideal shape of the relevant literature. This is caused by landscape, traffic and acquisition in the form of distortions of the hexagon geometry due to the non-ideal location of the base station. As a rule, the base station is nevertheless located at the center of the area served by it, subdividing the area into a maximum of six sectors.
The base stations are kept relatively low to the ground, i.e. below 50 m. High base stations are not considered since they cause high undesirable interferences when applying the above mentioned theories.
Omni-directional antennas are rarely used nowadays. Dual sectorization is used for straight-line coverage, such as road coverage and railway coverage.
From DE 100 06 621 A1 it is known that an antenna can be z-axis rotation symmetrically shaped. With this single antenna it is not possible to create sectorized cells according to existing standards such as GSM, TDMA, CDMA and UMTS.
From JP 2002186018A a system and method are known for dynamically varying traffic channel sectorization within a spread spectrum communication system. This enables varying the concentration of traffic channels in response to changes in the distribution of users within a spread spectrum cellular communications system. It does not provide a solution for creating radio coverage in an area.
From JP 2002107439A it is known that an arrival direction-estimating device can have eight directional antennas. These antennas are not suitable for creating radio coverage in an area.
The acquisition of UMTS licenses has been a great strain on the resources of telecommunication companies. There is a need to build an extensive UMTS radio network quickly, covering at least the bigger cities. There is however a lack of suitable sites to place base stations and there are considerable problems in subsequent negotiations for existing sites. Also there is a considerable loss of time due to necessary coordination with other parties and frequently repeated re-planning of the radio network.
Therefore an UMTS radio network construction will only be possible at a very slow pace and at great financial expenses. Moreover, it is expected that a network full of coverage holes will be the result.